Renewable energyRenewable energy is a source of energy that can never be exhausted.
We can obtain renewable energy from the sun (solar energy), from the water (hydropower), from the wind (windmills), from hot dry rocks, magma, hot water springs (geothermal) and even from firewood, animal manure, crop residues and waste (Biomass).

I just ran across an interesting article about renewable energy over at the Green Tech weblog. In it, they break down the type of investment that would be required to replace the energy provided by a cubic mile of oil (CMO).

In case you’re not aware (as I wasn’t), a CMO is a measure of energy consumption. Apparently the world consumes slightly more than one CMO worth of energy from oil per year, and the equivalent of three CMOs from all energy sources. Over 80% of this total energy usage comes from fossil fuels, including oil, coal, and natural gas (see graph, below).

So… What would it require to replace just one CMO of fossil energy per year?

Solar panels

Assuming annual electricity capture of 2.1 megawatts per solar panel, we’d have to place them on 4.2 billion rooftops. In other words, we’d have to install on them on 250,000 roofs per day for the next 50 years to have enough solar panels to offset our current annual oil usage (and this ignores things like coal; see below).

Wind power

What about wind power generators? You’d need 3 million to equal one CMO. That would require the installation of 1,200 per week for the next 50 years.

Hydroelectric power

A large hydroelectric dam can generate roughly 18 gigawatts of power per year. Thus, to offset one CMO of energy, we’d have to build 200 major hydroelectric dams. The problem? There aren’t enough rivers left in the world to dam up.

Solar thermal power

It would require 7,700 solar thermal plants to offset one CMO. That would require the construction of 150 plants per year for 50 years. Unfortunately, just one has been built in the past 15 years.

Nuclear power plants

It would take 2,500 nuclear power plants producing 900 megawatts to produce the equivalent of one CMO worth of energy. In other words, we’d have to build one a week for 50 years. It’s also worth noting that nuclear power isn’t exactly renewable.

The future of demand

Even if we decided to pursue one of the above options, it’s important to keep in mind that energy demand is continually increasing. According to Ripudaman Malhotra, a fossil fuels researcher at SRI International, world energy demand is expected to double to six CMOs within the next 30 years.

The good news here is that we still have time. Current estimates show oil reserves of roughly 46 CMOs, natural gas reserves totalling 42 CMOs, and coal reserves of 121 CMOs. These numbers increase further when you add in difficult to extract sources such as tar sands.

The bad news is that, beyond being non-renewable, these sources of energy also have a number of adverse environmental impacts, and burning more of them at a faster rate is just going to create more problems.

The way forward

Clearly, if we’re ever going to come anywhere near freeing ourselves from fossil fuels — an eventual necessity, as we’ll ultimately run out — it will require a tremendous investment, a variety of different technologies (likely including some that haven’t been invented yet), and an awful lot of conservation.

Unfortunately, we’re dealing with a problem on such a massive scale that minor changes won’t be enough. Consider, for example, that replacing 1 billion incandescent bulbs with compact fluorescent bulbs only saves 0.01 CMOs per year. Yes, it’s important to cut back wherever we can. In this case, however, baby steps won’t be enough.

It’s also important to keep in mind that all of the technologies listed above result in electricity production. Given that a large fraction of our energy consumption is currently non-electric, we’ll need a lot of other infrastructure changes to go along with this.